Stacked plate heat exchanger for a reforming reactor

ABSTRACT

A heat exchanger has a stack of thermally conductive plate elements, each having a wave-shaped cross sectional profile. The plate elements are connected in a fluid-tight manner along abutting wave profile regions to form first and second channel structures which are separated from each other in a fluid-tight manner. The wave profiles of the plate elements comprise at least two types of waves of different width: a first type of wave defines the channels of the first channel structure, and a second type of wave defines the channels of the second channel structure. The channels of the first channel structure have a larger passage cross section than the channels of the second channel structure.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This application claims the priority of German patent document 100 01 065.2, filed Jan. 13, 2000, the disclosure of which is expressly incorporated by reference herein.

[0002] The invention relates to a stacked plate heat exchanger of the type which is suitable for use in a reforming reactor.

[0003] Heat exchangers of this type in plate form (also known as “disc form”) are disclosed, for example, in International Patent Document WO 97/15798 (PCT/SE96/01339). They are in use for various applications, such as in reforming reactors for producing hydrogen by steam reforming of a hydrocarbon or hydrocarbon derivative in stationary or mobile installations, such as fuel cell vehicles, and in gas-heated evaporators.

[0004] Conventionally, the plate elements have a “wave” or corrugated profile with alternating ridges and grooves that generally form a uniform wave structure, in which the waves are of a single type. For example, they may be in the form of a sine wave, and follow one another periodically without an interval between them. This configuration leads to identical (or substantially identical) cross sections of the two channel structures which are separated with regard to fluid. They are formed by stacking of the wave-profile plate elements which are connected in a fluid-tight manner along the contact points. An associated medium can be passed through each channel structure (for example a transverse channel structure obtained as a result of the stack), in order to transfer heat from one medium to another via the thermally conductive plate elements.

[0005] For certain applications, a heat exchanger of the type described above, in which one channel structure has a significantly larger cross section than the other, is desirable; for example in order to obtain a compact reforming reactor suitable in particular for mobile applications, such as in fuel cell powered vehicles. In such applications, one channel structure forms a reforming reaction chamber and the other channel structure forms a temperature-control chamber for controlling the temperature of the reforming reaction chamber. The temperature-control chamber is responsible for the required supply or dissipation of heat to or from the reforming reaction chamber and, if required, may be designed in such a way that it fulfils an additional function. For example, it may form a catalytic burner or a CO oxidation stage which is in thermal contact with a reforming reaction chamber via the plate elements.

[0006] For the reforming reaction chamber, a channel structure of relatively large cross section is desirable, so that large amounts of catalyst material can be introduced in the form of a bed of pellets. On the other hand, a smaller cross section is sufficient for the temperature-control chamber. The latter may be designed, for example, so that it can be heated by a hot gas or temperature-control oil. Also, the smaller cross section is often even advantageous for achieving turbulent flow conditions.

[0007] One object of the invention is to provide a heat exchanger of the type described previously, which can be produced with relatively little outlay.

[0008] Another object of the invention is to provide such a heat exchanger which has channel structures of different cross section for at least two media which are to be brought into thermal contact with one another.

[0009] Finally, yet another object of the invention is to provide such a heat exchanger which, where necessary, is suitable in particular for producing a compact reforming reactor or evaporator.

[0010] These and other objects and advantages are achieved by the stacked plate heat exchanger according to the invention, in which the stack of plates comprises plate elements having wave profiles (that is, transverse cross sections) with at least two types of waves of different width. (As used herein, the term “width” refers to the cross-sectional area of a respective half-wave; i.e., the integral—or cross sectional area—beneath the associated wave curve.) One type of wave defines one channel structure, while the other type of wave defines the other channel structure.

[0011] The arrangement of the plate elements in the stack and the design of the wave profiles is selected so that the channel or channels of one channel structure have a larger cross section than those of the other channel structure. This can be achieved in a simple way by providing different widths of the two associated types of waves. As a result, as desired, two channel structures with different passage cross sectional areas are provided for two media which are to be brought into thermal contact with one another in a compact plate-type heat exchanger

[0012] In one advantageous configuration of the invention, which entails little manufacturing outlay, the wave profile having at least two different types of waves is provided by forming elongate parallel valleys or indentations in the plate element, with semicircular or trough shaped cross sections, which indentations are spaced at a lateral or transverse distance from one another. These indentations form the half-waves for one type of wave, while the resulting ridges in the area between the spaced-apart indentations form the half-waves of the other type of wave. The different widths for the two types of waves can be achieved, for example, by making the (transverse) width of the indentations significantly greater than the distance between indentations.

[0013] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 shows a longitudinal section through a stacked plate heat exchanger having four plate elements with a wave profile which comprises semicircular indentations; and

[0015]FIG. 2 shows a view corresponding to that shown in FIG. 1, but for a variant with a plate element wave profile which has indentations in the form of troughs.

DETAILED DESCRIPTION OF THE DRAWINGS

[0016] The stacked plate heat exchanger shown in longitudinal section in FIG. 1 comprises four plate elements 1 a, 1 b, 1 c, 1 d. which may for example be rectangular, and are stacked on top of one another. At their edge regions 2, they are drawn upwards in the form of a dish, and are laid inside one another and connected in a fluid-tight manner. In their region which is active in terms of heat transfer, inside the edge region 2, the plate elements 1 a to 1 d are provided with a wave profile, as can be seen in a central region 3 in FIG. 1. The central region 3, in the sectional plane shown in FIG. 1, is laterally adjoined by a distribution/collection channel 4, 5 with a channel longitudinal axis 6, 7 that runs parallel to the stacking direction. Outside the distribution/collection channel structure, the wave profile of the plate elements 1 a to 1 d extends all the way to the edge region 2 (not shown, for simplicity).

[0017] The wave profile of the plate elements 1 a to 1 d characteristically comprises two types of waves of different widths, (i.e., different cross-sectional area F1, F2). Specifically, in this example, in cross section the wave profile comprises semicircular indentations 8 (or, therefore with the same meaning, semicircular elevations), which are formed at a distance from one another in such a manner that a web-like, planar plate section 9 remains between each two edges 8 a, 8 b of adjacent indentations, which edges face towards one another. In this manner, the sequence of indentations 8 and planar plate sections 9 forms a wave structure with alternating, relatively wide half-waves 10 in the form of an arc of a circle and a relatively narrow, flattened half-waves 11. I.e., a hybrid wave structure of quasi-alternating wavelength.

[0018] The indentations 8 or elevations 9 are formed in the various plate elements 1 a to 1 d at the same lateral positions, so that in the plate-stacking direction indentations and elevations alternate with one another. Consequently, on one side the arc-shaped half-waves 10 of each inner plate element 1 b, 1 c bear against the arc-shaped half-waves 10 of one adjacent plate element, and on the other side the flattened half-waves 11 of each inner plate element 1 b, 1 c bear against the flattened half-waves of the other adjacent plate element. (See FIG. 1.) Along the contact lines or areas between the abutting arc-shaped half-waves 10 and the abutting flattened half-waves 11 formed in this way, the plate elements 1 a to 1 d are connected to one another in a fluid-tight manner, for example by soldering or welding, in the same way as in the edge region 2.

[0019] Consequently, this heat exchanger structure provides two channel structures, each with a plurality of channels 14, 15 through which medium can flow in parallel. The channels 14 of a channel structure are defined by two opposite semicircular indentations 8 and the channels 15 of the second channel structure are defined by two opposite flattened wave structure sections. Since the free cross section F1 of the semicircular indentations 8 is selected to be significantly greater than the free cross section F2 of the flattened wave regions between in each case two indentations 8, the passage cross section for the channels 14 of the first channel structure (which corresponds to double the free cross section) is correspondingly larger than that of the channels 15 of the second channel structure.

[0020] As can also be seen from FIG. 1, the design of the above-described wave profile means that the periphery of a plurality of channels of one channel structure adjoin each channel of the other channel structure. Thus, when the heat exchanger is operating, with a first medium being passed through the first channel structure and a second medium being passed through the second channel structure, there is effective transfer of heat from one medium to the other via the wave profile walls. It will of course be understood that, for this purpose, the plate elements 1 a to 1 d are made from a thermally conductive material, and have a variable thickness which can be selected depending on the application and may, for example, be small enough for the plate elements 1 a to 1 d to be formed from flexible sheets.

[0021] The heat exchanger shown in FIG. 1 may, for example, be used as a compact reforming reactor for generating hydrogen in a fuel cell vehicle. For this purpose, the first channel structure having the larger channels 14 is used as a reforming reaction chamber, for which the associated channels 14 are charged with a suitable catalyst bed. The second channel structure, having the narrower channels 15, may be designed as a catalytic burner, as a CO oxidation stage or simply as a temperature-control chamber for a suitable heat-transfer medium, such as oil, glycol, etc., in order to sufficiently heat the reforming reaction chamber channels. When it is designed as a CO oxidation stage, the second channel structure 15 is fed, for example, with a reformate gas for gas cleaning, i.e. for reducing the CO concentration by selective carbon monoxide oxidation.

[0022] In addition to efficient heat transfer, further advantages of the heat exchanger structure shown in FIG. 1 are the low level of manufacturing outlay and the high mechanical pressure stability as a result of the plate elements 1 a to 1 d being connected in internal contact with one another, combined with a relatively low weight. When a catalyst bed is introduced into the channels 14 having the larger passage cross section to produce a reforming reactor, it is possible, with a given overall size of the reactor, to achieve a high level of reforming conversion, since a large amount of reforming catalyst material can be introduced and the flow of process gas in the reaction chamber channels can be well distributed.

[0023] It will be understood that, instead of the four plate elements shown, the modular heat exchanger structure may comprise any other number of stacked plate elements, depending on the requirements. As an alternative to the reforming reactor function described above, the heat exchanger may also be used, for example, as an evaporator for dynamic evaporation of hydrocarbons that are used in a reforming reactor or elsewhere.

[0024]FIG. 2 shows a variant of the heat exchanger structure in FIG. 1, which differs from the latter in terms of the cross-sectional shape of the indentations. Specifically, in this case elevations or indentations 8′ in the form of troughs provide the wave profile of the plate elements, which forms the flow channels. Consequently, the associated wider half-waves 10′ in this example have a wide, flattened wave crest section, resulting in broader or diamond-shaped contact surfaces 12′, along which these half-waves 10′ of adjacent plate elements bear against one another. Unlike in the corresponding, somewhat punctiform or linear contact surfaces 12 from the example shown in FIG. 1, in the heat exchanger shown in FIG. 2 there are relatively wide contact-area webs 12′. In this region the plate elements may be provided with apertures 16, as shown in FIG. 2, without risk of losing the seal between one of the channels 14′ of larger cross section of the first channel structure and one of the channels 15′ of smaller cross section of the second channel structure. The apertures 16 provide fluid communication in each case between the channels 14′ of the first channel structure of larger passage cross section, which follow one another in series, parallel to the direction of stacking.

[0025] Otherwise, the variant shown in FIG. 2 has the same properties and advantages as those which have been described above in connection with the exemplary embodiment shown in FIG. 1, to which reference may be made.

[0026] It will be understood that, within the context of the invention, if necessary it is also possible to provide heat exchangers whose plate elements have a wave profile with three or more different types of waves. In that event, the associated half-waves differ in terms of their free cross section (i.e., their surface integral) but are of the same amplitude, so that, when two plate elements bear against one another, the half-waves of all the types of waves are in contact in a common plane, where they can be connected to one another in a fluid-tight manner to form a corresponding number of different channel structures.

[0027] By suitable selection of the wave profiles for the plate elements parallel to the plane of the plates, (i.e., perpendicular to the direction of stacking), it is possible, to produce different types of channel structure, depending on requirements. For example, it is possible to form a transverse channel structure with rectangular plate elements by providing the plate elements with suitable openings in the four corner regions, which form collection and distribution channels, and otherwise with a wave profile which is V-shaped when the plate elements are viewed from above, with two wave profiles of adjacent plate elements running in opposite directions in a V shape, which face towards one another in the stack and bear against one another. The wave profiles in this case preferably form a row of waves which follow one another in the longitudinal direction of the plate and have a V-shaped longitudinal extent between the two plate wide sides with a V arc region lying approximately in the longitudinal center plane of the plate. The V arc regions of the V waves face in the direction of one narrow side for one plate element and in the direction of the opposite narrow side for an adjacent plate element.

[0028] An alternative possibility is a flow channel structure which is in the form of a set of channels, once again with rectangular plate elements having openings in the corner regions which form collection and distribution channels. A wave profile is provided having a plurality of waves which, in their longitudinal direction, extend between diagonally opposite corner-side openings. In this case, the waves of two adjacent plate elements extend between two different openings of the two pairs of corner-side openings which lie diagonally opposite one another. As a result, two groups of channel sets are formed which are arranged alternately in the plate stack, run perpendicular to the direction of stacking, and each extend between an associated distribution channel and an associated collection channel. Thus, a first medium can be passed through one half of the channel-set layers in the stack and a second medium can be passed through the other channel-set layers which are arranged alternately with respect to the first half in the stack, so that the two media are brought into effective thermal contact. In the design with a flow channel structure in the form of sets of channels, it is possible to use wave profiles which comprise waves of different amplitude. It is then only necessary to ensure that the wave troughs of each one plate element are in linear contact, along their longitudinal extent, with the wave crests of the adjacent, facing plate element. For this purpose the waves of the adjacent plate element have correspondingly different amplitudes. For this embodiment, it is possible, for example, to use wave profiles having double hump waves.

[0029] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A heat exchanger comprising: a stack of thermally conductive plate elements, each having a wave profile, which plate elements are connected in a fluid-tight manner along abutting wave profile regions to form first and second channel structures that are separated from each other in a fluid tight manner, wherein: wave profiles of the plate elements comprise at least two types of waves, with different widths; in said stack of plate elements, a first type of wave defines at least one channel of the first channel structure and a second type of wave defines at least one channel of the second channel structure; and the at least one channel of the first channel structure has a larger passage cross section than the at least one channel of the second channel structure.
 2. A heat exchanger according to claim 1 , wherein the wave profiles comprise grooves which are spaced apart from one another by planar plate sections, and have a cross section which is one of semicircular and trough shaped.
 3. A heat exchanger, comprising a stack of alternating first and second thermally conductive plate elements having a plurality of elongate parallel ridges and grooves formed therein, wherein: said ridges of said first plate elements have a first transverse cross sectional shape and define a first transverse cross sectional area which is open in a first direction, and said grooves have a second transverse cross sectional shape different from said first cross sectional shape, and define a second transverse cross sectional area which is open in a second direction opposite said first direction; said second transverse cross sectional area is greater than said first transverse cross sectional area; ridges and grooves of said first plate elements are transversely space and aligned with ridges and grooves of said second plate elements, whereby ridges and grooves of adjacent stacked plate elements form first and second channel structures, respectively; and abutting surfaces of said ridges and grooves in adjacent plate elements in said stack are joined in a fluid tight manner, whereby said first and second channel structures are sealed off from each other.
 4. A heat exchanger according to claim 3 , wherein: said ridges are formed by a separation of said grooves; and said second cross sectional shape is one of undulating and trough shaped. 